Ayatollah Ali Khamenei's comments are seen as support for the foreign policy of Mahmoud Ahmadinejad, who faces a powerful conservative and two heavyweight reformists in the June 12 election.

BEIRUT — Iran's most powerful political and spiritual leader warned voters Monday against supporting pro-Western candidates in next month's presidential election, comments widely seen as supporting President Mahmoud Ahmadinejad's approach to foreign policy over those of his challengers.

"Those who submit to the enemies and bring shame on the nation should not come to power by the people's vote," Ayatollah Ali Khamenei said during a speech in the western town of Bijar.

"Those who, through paying lip service to the Western countries and arrogant governments want to secure a position for themselves . . . should not come to power," he said. "These are not valuable for the Iranian nation."

As the official guardian of the Islamic Republic and its political values, Khamenei plays a key role in defining the range of debate in Iran's political establishment.

His comments coincided with an uptick in harsh criticism of Ahmadinejad's foreign policy by candidates seeking to unseat him in the June 12 elections.

Over the weekend, former parliamentary speaker and now moderate presidential candidate Mehdi Karroubi blasted Ahmadinejad for questioning the Holocaust, arguing that the president's controversial rhetoric rallied countries to the cause of Israel and alienated potential allies.

Other candidates have begun to outline foreign policy programs starkly different from Ahmadinejad's approaches. Mohsen Rezai, a former commander of the Revolutionary Guard and a conservative challenger, argued this weekend for a more conciliatory relationship with the United States.

"My government will engage in a constructive and effective interaction with the U.S. administration should I win the presidential elections," Rezai said in an interview with an Iranian news agency during a campaign stop in the southern city of Bandar Abbas. "In foreign policy, I believe in convergence between countries."

Former Prime Minister Mir-Hossein Mousavi, the president's other leading challenger, said Monday that Ahmadinejad's government was cultivating relations with ideologically kindred countries in Latin America instead of forging ties with the nearby nations of the Caucasus, Central Asia and the Middle East.

"We have neglected civilizations in which Iran has played a role and moved toward Latin America," he said in remarks reported by Iran's Press TV. "We have forgotten cities we lost in wars between Iran and Russia and cling to countries such as Venezuela and Uruguay."

Competition in the presidential election has turned out to be exceptionally heated, with the powerful conservative and two heavyweight reformists squaring off fiercely against Ahmadinejad.

Fars, a news agency close to Ahmadinejad, reported on a recent poll that showed 54.5% of respondents supported the incumbent. But another poll, published by the Iranian Students News Agency, found that 32% of those surveyed would vote for a conservative and 21.5% for a moderate, with the rest undecided.

Under Iran's political system, if a leading candidate receives less than 50% of the vote, a runoff election is held between the top two vote-getters.